However, he admitted that achieving a target of an additional 325,000 visitors to Ireland -- or an extra 4pc -- next year would be difficult.

"Frankly I think that's optimistic but a good shot would be 250,000," he said.

The Gathering is the country's biggest ever tourist drive and aims to boost tourist numbers with special events throughout 2013.

Taoiseach Enda Kenny, whose speech launching the initiative was described as "slightly offensive" by Byrne, has also weighed into the row.

"I admire the work of Gabriel Byrne. He has been a fabulous ambassador for Ireland, but respectfully I disagree here," he said adding the initiative was a "very credible" proposal.

Mr Kenny pointed to the Navy/Notre Dame American football game held in Dublin recently, saying it was a "fabulous opportunity for Americans, in particular, to find and have a sense of place as to where their antecedents came from".

Failte Ireland, which is spearheading the project, said people will make up their own minds about The Gathering and any criticism was not going to deflect from their work.

Byrne -- who previously served as the cultural ambassador for Ireland in the US -- claimed people were "sick to death" of being asked to help out in what they regarded as a "scam".

"Most people don't give a s*** about the diaspora except to shake them down for a few quid," he said.

Byrne was speaking to Today FM's Matt Cooper whose 'The Last Word' show was on a visit to New York, paid for by The Gathering.

However, Mr McKeon said it was "outrageous" to suggest that the tourism initiative was a means of fleecing the Irish diaspora.

"He's a wonderful actor and I greatly admire him but what a rant. Why do people immediately jump on any initiative and call it 'fleecing tourists'?" he asked.

He said Ireland is competing for tourists against its European neighbours every year and The Gathering is an opportunity for it to stand out from the pack.

"Not everybody is going to agree. We are a nation known for a certain amount of begrudgery, so there will always be counter-opinions.

"The fact is a lot of this developed out of a sense when the bad times hit two or three years ago people said they wanted to do something to help the country. We thought this was an opportunity to create a vehicle for this to happen," he said.

Aer Lingus said it expects a "significant boost" from the US next year and will be adding an extra 112,000 seats on its transatlantic routes. It is also planning a major festival in September promoting Irish sporting culture.